The present invention relates to an electromagnetic clutch including a braking mechanism that prevents an inertial rotation and slip on the output side after power transmission is cut off.
An electromagnetic clutch including a brake that works at the time of power cutoff is disclosed in, for example, Japanese Patent Laid-Open No. 2013-234723 (literature). The electromagnetic clutch disclosed in this literature includes a rotor that rotates integrally with an input shaft portion, an armature facing the rotor, and a braking member located on the opposite side of the rotor when viewed from the armature. The input shaft portion rotates upon receiving transmitted power. The rotor forms part of a magnetic circuit that passes a magnetic flux of an exciting coil. The armature is supported, via a plurality of leaf springs, by a pulley that is rotatably supported by the input shaft portion via a bearing.
In this electromagnetic clutch, when the exciting coil is excited, the armature is magnetically attracted by the rotor, and the rotation of the rotor is transmitted from the armature to the pulley via the leaf springs. When the exciting coil changes to a non-excitation state, the armature is separated from the rotor by the spring force of the leaf springs and pressed against the braking member. When the armature is pressed against the braking member in this way, a braking force acts on the armature, and the pulley stops together with the armature.
The pulley includes a cylindrical portion fitted on the outer ring of the above-described bearing, and an inner flange radially extending inward from the cylindrical portion. The inner flange is located between the bearing and the rotor in the axial direction. One-end portions of the above-described leaf springs are fixed to the inner flange by rivets. The end of each rivet projects inside the cylindrical portion. To prevent the outer ring of the bearing from hitting the ends of the rivets, a plurality of projections that abut against the outer ring of the bearing from the rotor side are formed on the inner flange. These projections abut against the outer ring of the bearing, thereby holding the pulley unmovable in a direction opposite to the rotor. The plurality of projections are arranged in the rotation direction of the pulley. Holes used to insert the rivets through the inner flange cannot be formed at portions where the projections are formed, and are therefore formed between the projections adjacent to each other.
An electromagnetic clutch including a brake that works in a non-excitation state, like the electromagnetic clutch described in the literature, is required to further increase the braking force of the brake and a holding force to hold the pulley at a standstill. The braking force or holding force can probably be increased by increasing the number of leaf springs. In the electromagnetic clutch described in the literature, however, since the projections are formed on the inner flange of the pulley, and portions where leaf springs can be attached are narrow, the number of leaf springs cannot be increased.